During the past three decades, many diesel fuel performance additives have been developed and marketed to improve fuel lubricity, enhance engine performance, increase fuel economy, reduce tailpipe emissions and increase engine life. These diesel fuel performance additives are typically formulated by adding one or more organic compounds to a hydrocarbon base. These additives are generally mixed with diesel fuel at the 100-5,000 ppm level.
Many of the diesel fuel additives utilized to date, have been specifically designed to improve fuel lubricity. Lubricity refers to the ability of a fluid to minimize the degree of friction between surfaces in relative motion under load conditions. A lubricity value of a fuel can be measured by a standard test method, such as ASTM D6079 or D6751. ASTM D6079 is the preferred test method for evaluating the lubricity of diesel fuel which is commonly referred to as the high-frequency reciprocating test procedure (HFRR). The wear scar generated in the HFRR is measured in terms of a diameter of wear scar in microns. Smaller wear scars are directly related to better fuel lubricity.
The combustion of fuels high with sulfur, for example, in conventional middle distillates such as diesel fuel and jet fuel, is considered a serious environmental problem because the sulfur is emitted as sulfur oxides which contribute adversely to airborne particulates and acid rain. Therefore, government regulations have been promulgated that significantly limit the amount of sulfur which may be present in such fuels. In the present context the terminology “low sulfur-content fuels” are intended to mean fuels typically having a sulfur content of less than 50 ppm by weight and more preferably less than 15 ppm by weight. Other fuels that have poor lubricating properties include synthetic diesel fuels that are produced from the hydro-processing of waxes formed from the catalytic conversion of syngas (H2 and CO).
Unfortunately, diesel fuels with low lubricity can cause excessive wear to engine components and damage to fuel pumps and injectors. Therefore, lubricity additives are blended with most commercially available diesel fuels.
A number of diesel fuel lubricity additives have been previously formulated and used to enhance lubricity performance characteristics. However, as established below, the high-performance additive outlined in this present teaching is very different from the currently available additive formulations that have been published in the patent and scientific literature.
It has been known since the early 1990's that C12-C30 fatty acid esters and fatty acids are good diesel fuel lubricity additives when added in sufficient quantities, typically greater than 500-10,000 ppm. Several recent formulations have been developed that utilize these fatty acids and fatty acid esters as a base with the addition of other chemical constituents to improve additive performance.
For example, U.S. Pat. No. 6,793,695 describes a lubricity additive containing fatty acid esters containing 8 to 24 carbon atoms and the addition of a hydrocarbyl monoamine or hydrocarbyl-substituted poly alkylene-amine to increase additive performance.
U.S. Pat. Application Pub. No. 0132641 describes a lubricity additive that is based upon the reaction products of saturated, unsaturated, mixed saturated and unsaturated di- and tri-carboxylic acids having from 12 to 72 carbon atoms with hydroxyl compounds selected from the group consisting of alcohols, glycols and poly-glycols. The resulting formulation is a mixture of esters which are proposed as lubricity additives.
One of the problems with using fatty acids and fatty acid esters as lubricity agents is that they can cause engine problems (Pillay, 2012) such as engine deposits.
The high-performance additive described in this application does not require the use of any fatty acid or fatty acid esters as described in the above prior art.
U.S. Pat. Application Pub. No. 0288638 A1 describes a fuel lubricity additive that incorporates a mixture of at least one alicyclic amine and at least one fatty acid, having between eight and 22 carbon atoms.
U.S. Pat. No. 5,194,068 discloses fuel compositions containing small amounts of an ester of a mono- and/or poly-carboxylic acid with an alkyl alkanol-amine or alkyl amino-polyalkylene glycol.
U.S. Pat. No. 6,001,141 describes a diesel fuel additive that contains a carboxylic acid substituted by a least one hydroxyl group, derivatives of the carboxylic acid substituted by at least one hydroxy group, and an ester which is the reaction product of a carboxylic acid which does not contain any hydroxy substitution in the acid backbone and an alkanol-amine.
U.S. Pat. No. 7,182,795 B2 describes a diesel fuel additive that is synthesized from the chemical reaction of a hydro-carbonyl succinic anhydride and a hydroxy-amine.
The high-performance additive described in this application does not require the use of alicyclic amines, alkyl alkanol-amines or alkyl amino-polyalkylene glycols as described in the above prior art.
U.S. Pat. No. 7,867,295 describes a diesel fuel additive that utilizes highly branched carboxylic acids (e.g. trialkyl acetic acid and dimethyl propionic acid) dissolved in aromatic solvents. This additive formulation faces some major challenges as follows: 1) These di-methyl and tri-methyl-branched C3-C14 carboxylic acids have limited solubility in aromatic solvents; 2) Many of these branched acids are not commercially available and/or costly; and 3) These branched acids have difficulty forming chemical bonds with iron surfaces due to steric hindrance from the methyl groups on the acids.
Berlowitz (U.S. Pat. No. 6,017,372) describes the formulation of additives that employ esters, polyols, alkenes and aldehydes. However, the additive described herein does not contain these organic mixtures.
MacMillan (U.S. Pat. No. 6,156,082) describes a formulation to improve diesel fuel lubricity which employs mixtures of C10-C32 alkenes (e.g., olefins) substituted with alkyl ethers. A major problem with such formulations is that alkenes degrade (oxidize) rapidly under typical friction conditions, reducing their effectiveness.